Background / aims. Pseudomonas aeruginosa is an opportunistic pathogen that secretes molecules called pyoverdines, which chelate iron and deliver it into the bacteria via specific receptors. There are three chemically distinct classes of pyoverdines. The genes required for pyoverdine synthesis and uptake are well characterised and are amongst the most variable within this species with only ~30% identity between types. The aim of this research was to investigate the role of horizontal gene transfer in generating genetic diversity at the pyoverdine locus.

Methods. Over 1400 genome sequences of P. aeruginosa from publicly available databases were examined for phylogenetic relatedness, pyoverdine type and recombination analysis using RAxML and Gubbins.

Results. Each genome was found to encode only one of the three types of pyoverdine. Whole genome phylogenetic analysis showed that strains do not cluster according to pyoverdine type indicating horizontal transfer of genes for pyoverdine synthesis and uptake. Recombination analysis revealed the pyoverdine locus as one of six within the P. aeruginosa genome that had a high rate of recombination. The pyoverdine locus itself has five regions that have a high rate of recombination that not only include type specific genes but also genes that are highly conserved between types.

Conclusion. Our findings demonstrate the very extensive role of horizontal gene transfer and recombination in the phenotypic evolution of a bacterial pathogen.